Columbium base alloys



United States Patent Ofiice 3,086,859 Patented Apr. 23, 1963 3,086,859 COLUMBIUM BASE ALLOYS Richard A. Jefterys, Euclid, Ohio, and Warren 1. Pollock and Frederic J. Anders, In, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Aug. 30, 1960, Ser. No. 52,768 6 Claims. (Cl. 75-174) This invent-ion relates to columbium-base alloys containing small amounts of carbon.

Columbiumbase alloys are known for their high-temperature strength and for their high-temperature oxidation resistance. The present invention is concerned with the discovery that if a small but critical amount of carbon is present in columbium-base alloys, it has the effect of significantly raising the embrittlement temperature of such alloys; i.e., for any given period of time, the alloys of this invention are able to withstand considerably higher temperatures without becoming embrittled. As a result of the use of carbon in the amounts herein specified in columbian-base alloys, it is possible to work and weld these alloys more readily and to utilize them at much higher temperatures than was previously possible.

' The columbium-base alloys in which carbon can be used to raise the embrittlement temperature are those containing titanium and either molybdenum or tungsten, or mixtures of molybdenum and tungsten. The amount of carbon required is 0.02%-0.2% by weight of the alloy, with a range of 0.05 %-0.15 being preferred.

Preferred alloy compositions possessing good hightemperature strength and oxidation resistance which are improved by the addition of 0.02%0.2% of carbon are those containing 7-13% titanium, 718% molybdenum, the balance being essentially columbium. In these compositions, all or a portion of the molybdenum may be replaced on an atom-for-atom basis by the element tungsten.

Expressing these limitations in terms of weight percent compositions, the alloys of this invention comprise 0.02%0.2% carbon, 713% titanium, and one of the group consisting of 1) 7-18% molybdenum, (2.) 10'- 34% tungsten, and (3) 734% of a mixture of molybdenum and tungsten in which the molybdenum content is not greater than 18% of the total alloy composition, the balance being essentially columbium in an amount of at least 50%.

In a more specific embodiment, the alloys of this invention comprise 0.02%-0.2% carbon, 713% titanium, 7- 18% molybdenum, the balance being essentially columbium.

In another embodiment, where tungsten replaces a portion of the molybdenum, the alloys comprise 0.02%- 0.2% carbon, 7-13% titanium, 27% molybdenum, 15- 30% tungsten, the sum of the molybdenum and tungsten being 7-34% of the total and the balance being essentially columbium.

In still another embodiment, where tungsten replaces all of the molybdenum, the alloy comprises 0.022% carbon, 7-13% titanium, 15-30% tungsten, the balance being essentially columbium.

The alloys which are herein described can be prepared by conventional procedures, such as by powdered metallur-gy or by melting and casting techniques. For example, the individual metals can be melt-cast together and the melt [allowed to cool and solidify into a desired shape. The required amount of carbon may be added in any convenient form, as for example lampbl-ack, or graphite; or it may be added in combination with one of the metals used, as for example columbium carbide, titanium carbide, molybdenum carbide, or tungsten carbide. The

melting operation can be carried out in an arc melting furnace provided with consumable or nonconsumable electrodes, or by subjecting the charge to induction heating in a skull or specially designed crucible type of container. One useful form of arc melting furnace comprises that having an integral, water-cooled copper crucible in which the charge can be melted, and solidified, such as that described by W. Kroll in Transactions of the Electrochemical Society, vol. 78, pages 35-47, 1940. Alternatively, a compressed, consumable arc electrode type melting furnace can be employed, such as described in U.S. 2,640,860 to S. A. Herres, as can the combination of a nonconsumable and consumable electrode type of double melting furnace described in U.S. 2,541,764 to S. A. Herres. A continuous-feed type of furnace can also be used, such as described in U.S.P.B. Report 111,083. Whatever the type of furnacing means employed, care should be exercised in the melting and casting operation to protect the molten metal from normal atmospheric contamination through contact with oxygen, nitrogen, etc. Contamination can be prevented by conducting the operation under a vacuum or an atmosphere of an inert gas, such as argon, helium, etc.

The individual metals charged to the melting furnace can be in any desired form, e.g. powder, grains, shot, wire, or sponge, and should be of commercially acceptable purity to insure production of a satisfactorily pure alloy product. Although preferably metals exhibiting relatively high purity are utilized herein, some variance in purity properties can be tolerated. Residual amounts of carbon are usually found in one or more of the metals used to prepare the alloy compositions. Therefore, it is pointed out that this residual carbon content of the alloy should be taken into consideration in adjusting the amount of carbon to 0.02%0.2%. The alloys of the examples and those tested were prepared from commercially available columbium, titanium, and molybdenum. The carbon was added in some cases as commercially available columbium carbide, and in some cases as commercially available graphite.

For a clearer understanding of the invention, the following specific examples are given. These examples are intended to be merely illustrative of the invention and not in limitation thereof. All percentages are in terms of weight and all tensile tests are according to the recommendations of the ASTM, Designation E8-5 4T.

EXAMPLE 1 An alloy of 10% Ti, 10% Mo, 0.025% C, balance Nb was prepared by melting together in an atmosphere of helium in a water-cooled, copper crucible of an arc-melting furnace 395.6 parts of columbium, 50.0 parts of titanium, 50.0 parts of molybdenum, 4.37 parts of columbium carbide. When the metals had become completely molten, the furnace was turned 01f and the melt was allowed to solidify and cool in the helium atmosphere. The alloy was then remelted and resolidified six additional times in order to insure thorough mixing of the ingredient metals. The casting was ultimately recovered in the form of the water-cooled copper crucible. The casting was machined to a round bar of approximately /2" diameter x 5".

In the same manner, other alloy samples were prepared in accordance with the compositions listed in Table I below. Each of the alloy samples prepared by melting and machining as described above was then swaged through a series of dies at the specified temperature, each die reducing the cross-section by 12 /2%. The results are given in Table I below.

3 4. Table 1 material 1350 C. at an extrusion ratio of approximate- INFLUENCE or CARBON ADDITIONS ON WORKABILITY f 6 to Part of thls extruslon was maQhmed diameter and swaged at 1000 C. to approximately 70% Composition (percent) Reduction in cross-sectional area reductlon In Press Sectlonal area: Speclmens of thl s wit o c a (p swaged material were heat treated in vacuum at the various temperatures specified in Table III and tested at room Nb T1 Mo 0 S ed a Swaged at Swaeed at temperature. The results of these tests are given in Table 1,000 0. 1,400 0. 000 C. In

An alloy of the same composition except that no car- Egi: V g g g2 32 5(8) 5g bon was added was similarly melted, extrudg d, and tested. 3? i8 18 g 823 g8 g8 g3 Resu ts of t ese tests are also lncluded 1n able III. B31: 10 10 0:25 25 40 Table HI 1331- 10 10 (9 (1) 1 INFLUENCE OF HEAT TREATMENT AND 0 ADDITIONS (1) 0) 0 5 ON PROPERTIES OF EXTRUDED ALLOYS 1 Severe cracking. 2 Residual; not intentionally added. Strength Ductility EXAMPLE II 02178 Utltinriltc 11Eercet1i1t Pgrcetnt A series of alloy compositions was made up in the H1516 eqnga 011 I6 no 1011 .1. 3 1 manner described in Example I and machined into bars (P31) (P S IDA approximately /2" in diameter x 5". These bars were heated in an electric furnace at 1100 C. and swaged to 10% T1, 10% Mo, 0.08% O,

1 5017 d 1 10211. Nb: approxunatey 0 re uction 1n cross sec iona area. After Swagmg no heat The alloys were then heated in a vacuum induction furtreatment 113, 000 124, 900 10 a0 nace for the times and at the temperatures given in Table izggs 8: 2?: g: H. After this heating, the alloy samples were tested at 1hr. at1,600 0. 89,800 00,400 32 53 room temperatures for strength and ductility.

T bl H NOTE.10% Ti, 10% Mo, bal. Nb: 1 hr. at 1,400 O.-En1brittled.

a 3 Failed in tensile testing before yield strength was reached.

INFLUENCE'OF HEAT TREATMENT ON PROPERTIES OF SWAGED C-CONTAINING ALLOYS EXAMPLE IV s h D Part of the extruded stock from Example 11 was forged trengt uctihty to approximately 0.1 0" sheet. The surfaces of the forg- 2 UW t P t P ing were cleaned and the sample was heat treated in $1 K; gg; 323 gffgfg vacuum for 1 hour at 1400 The heat-treated sample (0 (I 1n /1 in ss was cold rolled to 0.040" strip and the rolled strip was heat treated a second time at 1400 C. for 1 hour. A room temperature bend test was then made. The sample ?5 P 10% was bent 180 Without cracking.

ffiheatltgeaggment v 23.1 180 2;, 18g 3 A similar alloy sample but containing no added carbon 1 3', 1 8 0 mg 983400 20 22 was melted, extruded and forged in the same manner. gm m ti0$8 38 35,400 3- 2-2 The sample was heat treated for 1 hour in vacuum at m fij f, sf 1400 0. An attempt was made to cold roll the heatt 95 000 102.000 20 55 treated sample, but it cracked badly and could not be fi men 931000 28 58 rolled to sheet. An additional sample of the same alloy %hr. l,4i%? g $8 without heat treatment was rolled to 0.040 sheet. This 5 3: C 173 7 strip was then heat treated for 1 hour in vacuum at 1400 C. at room temperature and in a bend test the sample 'iqg h treatment 5 broke immediately on loading.

300 11 i. 2.. 15 6 EXAMPLE v 1 r. 24 4s. 1 hr, 11 11.5 An alloy bar of 10% T1, 10% Mo, 0.10% C, balance g g $31; columbium was prepared according to the procedure described for Example I. The alloy bar so prepared was The advantageous effect on these alloys of carbon addi heated n an electric furnace and rolled to 0.100 sheet. fibn Within the ran 6 S ecified in this invention ma be The strip was ground to 0. 060 and heat treated for one seen by comparison of t heseresults with those iven be hour at 14000 Two sections of this Sheet Wars 6160 low, for an alloy, containing 0 005% C which p tron-bea-m welded in a vacuum of less than 10* mm. Hg with 15 kllovolts and 105-110 mrlllamps. at a welding pared and tested In the same manner as set forth above. Speed of 49 inches per minute. Rectangular specimms i were cut from the welded material so that the weld bead Strength Ductillty was transverse to the specimen axis. At several temperatures, the specimens were bent around a mandrel, with the 0.2% Ultimate Percent Percent mandrel directly beneath the weld bead, to determine the f iil gg ggg g minimum temperature at which a bend could be section obtained without fracture; A transition from ductile (90 bend) to brittle (less than 40 bend) occurs at 1381. Nb, 10% Ti, 10% M0, 75 C.

flg-fgggi ggggg 97,000 104,000 25 48 An alloy sample of similar composition but with no 1 hr. 1,400 C 81,500 82,000 2 2 carbon added was tested in the same manner. The transition temperature was found to be +55 C.

EXAMPLE I'II EXAMPLE 1 AH l y of 10% Ti, 10% Carbon, PalanCe An alloy sample of 10% Ti, 10% Mo, 0.05% C, bal columbium was prepared by consumable arc-melting. A ance columbium was prepared for welding as given in 3" billet of this composition was extruded at approxi- Example V. The sheet in this case was rolled to 0.040"

and was electron beam welded in a vacuum of less than mm. of Hg with kilovolts and 45 milliamps. at a welding speed of 22 inches per minute. Rectangular specimens were cut from the welded material so that the weld bead was transverse to the specimen axis. At several temperatures, the specimens were bent around a mandrel, with the mandrel directly beneath the weld bead, to determine the minimum temperature at which a 90 bend could be obtained without fracture. A transition temperature of 150 C. was found for the alloy of this example. The transition temperature of an alloy of the same composition but without the added carbon was found to be C.

EXAMPLE VII Part of the extruded stock from Example III was forged into a plate to approximately 0.100 thick. The surfaces of the plate were cleaned and the sample was heat treated in vacuum at 1400 C. The heat-treated sample was cold rolled to 0.04" strip. One piece of the rolled strip was heat treated in vacuum for one hour at 1400 C., and another piece Was heated for one hour at 1500 C. Both specimens showed 23% elongation (in /1" gauge length) in room temperature tensile tests.

EXAMPLE VIII Alloys having the composition set forth in Table IV were prepared by arc-melting. 3" billets were then extruded at 1550 C. at an extrusion ratio of approximately 621. The extruded alloys were swaged at 1100 C. to 70% reduction in cross section area. Portions of these swaged materials were heat treated in vacuum for the times and at the temperatures given below and were tested at room temperature. The results of these tests are given in Table IV.

Table IV INFLUENCE OF HEAT TREATMENT ON DUCTILITY OF Nb-Ti-Mo-W-C ALLOYS Strength Ductility 0.2% Ultimate Percent Percent yield tensile elongation reduction (p.s.i.) (p.s.i.) 3 in cross section Bal. Nb, 10% T1, 6% Mo, 20%, W, 0.0065% 0 (residue 1 hr. at l,300 C 135,800 145, 300 l 9 1 hr. at 1,400 O Bal. Nb, 10% Ti, 6% Mo, 20%, W, 0.005% O (resid- 11a 1 hr. at 1,300" O 143, 900 153,800 1 10 1 hr. at 1,400 0 130,000 132, 400 4 6 Hal. Nb, 10% Ti 6% Mo,

1 hr. at 1,300 0-- 127, 400 139, 900 17 30 1 hr. at 1,400 C 118, 400 127,300 12 15 1 hr. at 1,500 0-- 117, 400 123, 000 9 13 1 Approximately. 2 Specimen broke into several pieces. I Broke before yield strength was reached.

It 'will be seen from the above examples that extremely valuable alloys have been produced by the addition of small amounts of carbon to columbium base alloys comprising titanium, molybdenum, and tungsten. By the application of this invention to high-temperature oxidationresistant alloys, it has been possible to increase the time and temperature of service of such alloys.

The alloys of this invention will be found particularly valuable in applications where a highly fabricable, ductile, strong, and oxidation-resistant material is required. Particularly, the alloys will be found useful where equipment is to be used at high temperatures, and in which it is especially desirable to retain such properties as strength and ductility at low temperatures after high-temperature service. The alloys herein described are exceptionally useful in applications requiring sheet and in which cupping, forming, and welding are necessary. The alloys of this invention have been found particularly suitable for use in high-temperature equipment, such as turbine vanes, flame holders, high-speed aircraft skin, after-burner liners, and chemical reactors and their accessories.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

The embodiments of the invention in which an ex elusive property or privilege is claimed are defined as follows:

1. A columbium-base alloy consisting essentially of, by weight, 0.02%-0.2% carbon, 7-13% titanium, and one of the group consisting of 1) 7-l8% molybdenum, (2) 1034% tungsten, and (3) 7-34% of a mixture of molybdenum and tungsten in which the molybdenum content is not greater than 18% of the total alloy composition, the balance of this alloy composition being essentially colurnbium, the amount of said columbium being at least 50% of the total alloy.

2. A colurnbiumbase alloy consisting essentially of, by Weight, 0.02%0.2% carbon, 713% titanium, 7l8% molybdenum, the balance being essentially columbium.

3. A columbium-base alloy consisting essentially of, by weight, 0.02%-0.2% carbon, 713% titanium, 27% molybdenum, 15-30% tungsten, the sum of the molybdenum and tungsten being 17-34% of the total, the balance being essentially columbium.

4. A columbium-base alloy consisting essentially of, by weight, 0.02%-0.2% carbon, 7-13% titanium, 1530% tungsten, the balance being essentially columbi'um.

5. A columbium-base alloy consisting essentially of, by weight, 0.02%-0.2% carbon, about 10% titanium, about 10% molybdenum, the balance being essentially columbium.

6. A columbium-base alloy consisting essentially of, by weight, 0.02%0.2% carbon, about 10% titanium, about 6% molybdenum, about 20% tungsten, the balance being essentially columbium.

References Cited in the file of this patent UNITED STATES PATENTS 1,588,518 Brace June 15, 1926 2,822,268 Hix Feb. 4, 1958 2,877,112 Thielemann Mar. 10, 1959 2,882,146 Rhodin Apr. 14, 1959 

1. A COLUMBIUM-BASE ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT, 0.02%-0.2% CARBON, 7-13% TITANIUM, AND ONE OF THE GROUP CONSISTNG OF (1) 7-18% MOLYBDENUM, (2) 10-34% TUNGSTEN, AND (3) 7-34% OF A MIXTURE OF MOLYBDENUM AND TUNGSTEN IN WHICH THE MOLYBDENUM CONTENT IS NOT GREATER THAN 18% OF THE TOTAL ALLOY COMPOSITION THE BALANCE OF THIS ALLOY COMPOSITION BEING ESSENTIALLY COLUMBIUM, THE AMOUNT OF SAID COLUMBIUM BEING AT LEAST 50% OF THE TOTAL ALLOY. 